The invention relates to a device for reducing the sealing gap between a rotating component and a stationary component inside a rotary turbo-engine through which a flow passes axially and in which the rotating component and the stationary component each have a surface portion arranged separated by a sealing gap and providing sealing structures on at least one of the two surface portions, one of the sealing structures being an abradable planar sealing structure.
In the attempt to optimize the efficiency of rotary turbo-engines, for example compressor units and in particular gas-turbine stages, any processes resulting in losses are as far as possible completely eliminated or at least minimized. Processes resulting in losses are caused inter alia by sealing gaps between the rotating component and the stationary component of a plant which have to be set to the minimum in order to reduce the leakage flows which pass through the sealing gaps and which do not assist the energy conversion.
Labyrinth seals are known from gas-turbine technology; they comprise intermeshing sealing strips and are each attached to mutually opposed surface portions of the rotating and stationary components of the plant and in turn help to minimize the leakage flows. In addition, rib-shaped, step-shaped or honeycomb-shaped sealing structures are known which are used to reduce the sealing gap in the same way. FIG. 2 with its alternative illustrations a to e shows conventional, known sealing structures and their combinations. In all the illustrations of FIGS. 2a to 2e it is to be assumed that the upper component 1 rotates relative to the lower component 2 of the plant. In the case of FIG. 2a the surface portions 3 and 4 form a sealing gap 5 and, in addition, on their surfaces they have web-like, mutually intermeshing raised portions 6 which form a labyrinth seal known per se. In FIG. 2b the surface portion 3 of the rotating component 1 has three rib structures 8 attached to it, opposite which is arranged a honeycomb structure 7 which is secured to the stationary component 2. In this case the sealing gap 5 is bounded locally by the narrow points between the rib structures 8 and the honeycomb structure 7.
In order to be able to set to a minimum the distance between the rib structures 8 and the surface 71 of the sealing structure 7 which is attached to the surface portion 4 of the stationary component 2, as shown in FIG. 2c the planar sealing structure 7 is constructed in the form of an abradable layer 9 so that the rib structures 8 which usually have an abrasive effect wear the abradable layer 9 locally during contact, as a result of which a minimal sealing gap is formed between the rib structures 8 and the surface 91 of the abradable layer 9. In addition, it should be mentioned at this point that the honeycomb structure can also have abradable properties.
In addition, stepped sealing-gap structures are known, as may be seen in FIGS. 2d and 2e, in which the rotating component 1 and the stationary component 2 have stepped surface portions with corresponding sealing structures. In FIG. 2d rib structures 8 are again attached opposite planar honeycomb structures 7, whereas in FIG. 2e rib structures 8 are arranged opposite abradable layers 9.
Irrespective of the multiplicity of known designs of sealing structures and the known combinations thereof, the desire nevertheless remains to have improved possibilities of reducing the sealing gap or of reducing the leakage flow occurring through the sealing gap.
The object of the invention is to design a device for reducing the sealing gap between a rotating component and a stationary component inside a rotary turbo-engine through which a flow passes axially and in which the rotating component and the stationary component each have a surface portion arranged separated by a sealing gap and providing sealing structures on at least one of the two surface portions, one of the sealing structures being an abradable planar sealing structure, in such a way that the flow resistance through the sealing gap is to be further increased and the leakage flow associated therewith is to be significantly reduced. In addition, the steps to be taken should not necessitate a substantial outlay in either structural or financial terms.
If solutions known per se for reducing leakage flows between stationary and rotating components inside a rotary turbo-engine are considered, it is evident that a mutually adjacent arrangement of raised portions designed in the manner of webs or ribs can always be observed on at least one of the two mutually opposed components, as a result of which swirling is induced inside the leakage flows, so as to increase the flow resistance inside the sealing gap in this way. The flow swirls are formed, in particular, immediately downstream of the passage of the leakage flow through the narrow gap behind a rib and, at the same time, produce a perceptible throttling action upon the leakage flow passing through the narrow gap.
In contrast to the known arrangement of sealing structures as described above, the invention is based on the knowledge that greater throttling loss in the leakage flow can be caused by the structural provision of a long and narrow sealing gap between the two components movable relative to each other than is the case with conventional sealing structures using projecting rib structures.
Surprisingly, tests have shown that a long and narrow sealing gap, which preferably has a constant minimal sealing dimension in the direction of flow, has considerably better throttling characteristics with respect to the leakage flow than rib structures which are arranged in succession in the direction of flow and which each can enclose a respective narrow gap in the same order of magnitude.
In order to be able to adjust the setting of a minimal sealing gap between two planar sealing structures, the sealing structures are made abradable, so that when they are in mutual contact by corresponding abrasion they form a sealing gap with a minimal dimension.
According to the invention, therefore, a device for reducing the sealing gap according to the preamble of claim 1 is designed in such a way that the surface portion opposite the abradable planar sealing structure likewise has an abradable planar sealing structure and that the two sealing structures bound the sealing gap in a planar manner.
In a preferred embodiment the device according to the invention for reducing the sealing gap provides two directly opposed planar honeycomb structures as abradables, which are mounted in each case on the rotating and stationary components respectively of the rotary turbo-engine and form a planar narrow sealing gap between themselves. The mutually opposed honeycomb structures have open honeycomb bodies whichxe2x80x94on the basis of the current understanding of the throttling effectxe2x80x94contribute in an advantageous manner to the improved throttling action. If a leakage flow occurs in the minimal gap between the mutually opposed honeycomb structures, micro-swirls occur directly on the surface of the individual honeycomb structures and penetrate into the openings of the individual honeycomb openings and are trapped there in the normal manner. In view of the multiplicity of the honeycomb bodies which are opened towards the sealing gap and which in addition bound the sealing gap on both sides, it is possible for the micro-swirling effectxe2x80x94occurring at each individual honeycomb openingxe2x80x94in its entirety with respect to all the honeycomb bodies bounding the sealing gap to throttle or reduce the leakage flow highly effectively.
As an alternative to the usexe2x80x94described abovexe2x80x94of planar honeycomb structures as sealing structures, layers of abradable material, which bound the sealing gap between a rotating and a stationary component inside a rotary turbo-engine with a minimal sealing gap, are likewise suitable.
In a manner comparable with the situationxe2x80x94described abovexe2x80x94by the provision of honeycomb structures, it is advantageous in the case of so-called abradable planar layers of material if the layers of material have a surface which encloses the sealing gap and which [has] a specific surface roughness or is provided on its surface with a suitably applied micro-surface texturing by which it is possible to produce a micro-swirling of the leakage flow passing through the sealing gap.
Layers of material of this type which are also suitable as abradables are for example MCrAlY material layers which can be applied to the corresponding surface portions of the rotating and stationary components by means of flame spraying and, depending upon the material and flame-spraying parameters selected, have a porosity which results in the desired surface roughness.
By means of the knowledge, according to the invention, of bounding the sealing gap with the aid of planar abradables which result in greater throttling loss than is the case with the rib-like sealing structures known hitherto, sealing structures are possible which are particularly easy to produce and inexpensive to manufacture.